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Chapter 4 — Calculation Method

(This section was marked "to be added" in the printed Fifth Edition manual. The summary below is drawn from Chapter 1 and the current GATB source code.)

Overview of the GATB Calculation Pipeline

GATB is a graphical HVE front-end for the ATB (Articulated Total Body) rigid-body dynamics program (this version is based upon ATB-V.1, June 1998). The calculation proceeds as follows (verified against Physics/Source/GATB/):

  1. Data extraction — GATB extracts the human, vehicle, environment and event data from HVE (GATBinput.cpp) and writes a complete ATB input file (gatb.ain), automatically selecting the appropriate ATB options, card images (A-, B-, C-, D-, F- and H-cards), contact panels, belt/harness and airbag data.
  2. ATB solution — The embedded ATB solver (the Fortran routines in Physics/Source/GATB/*.for, built as the GATB Fortran function library) integrates the equations of motion of the 15-segment, 14-joint articulated body. Segment-vs-panel, segment-vs-segment, belt and airbag forces are evaluated each time step. GATB hard-codes the ATB integration time step at a fixed 0.002 sec (GATBinput.cpp:538, ATBTimeStep = 0.002f, written into the %8.5f field of the A4 card at GATBinput.cpp:563); the number of steps is derived from Tmax / 0.002. The other values on the A4 card (.00050, .00100, .0000625) are ATB minimum-time-step and print/integration-control fields — the .00050 is not a "human-collision" step. Within each step the integration is handled by the variable-step Runge-Kutta/predictor-corrector integrator internal to ATB (dintg.for, daux*.for).
  3. Output return — The solver's standard output (gatb.aou), structured output (.sal) and time-history (tape 8) files are read back (GATBoutpt.cpp, read_tape_8.for) and converted into the HVE reports described in Chapter 3 (Accident History, Human Data, Injury Data, Program Data, Results, Vehicle Data, Variable Output and Trajectory Simulation).

The human model is the HVE human data set: 15 mass segments, each with up to 3 contact ellipsoids, connected by 14 joints (up to 4 joints attach to a single segment) — see Physics/Include/HUMAN.H. Injury measures (HIC, HSI, CSI) are computed by the ATB post-processor (postpr.for, hiccsi.for).

For the underlying theory of the ATB model — the equations of motion, joint models, contact force model and restraint (harness and airbag) models — see the four-volume CVS/ATB documentation and the ATB-V.1 documentation listed in Chapter 7, Technical References.

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